The present invention relates to a fluid pressure operated control system for controlling the position of a vehicle auxiliary device, and more particularly, to such a control system for controlling a device which is subject to varying loads throughout its range of displacements.
Although the fluid control system of the present invention may be used advantageously with many different types of vehicles and vehicle auxiliary devices, it is especially suited for use in controlling aircraft flaps and slats, and will be described in connection therewith.
Typically, aircraft flap and slat drive systems have been primarily hydraulic systems, and have utilized fixed displacement hydraulic motors as the means for directly actuating or driving the aircraft flaps.
Although the prior art systems, utilizing fixed displacement hydraulic motors, have been generally satisfactory in terms of performing the basic function of driving the flaps, the prior art system has had certain inherent drawbacks. It should be noted that these drawbacks are not peculiar to aircraft flap drive systems, but are also applicable to various other hydrostatic drive systems which operate to change the position of a device which is under varying load conditions, as it moves throughout its range of displacement.
A key operating criteria for an aircraft flap drive system is the ability to achieve full stroke (i.e., full movement of the flap) within a specified time period, and with the flap subjected to the specified load profile. In a flap drive system utilizing a fixed displacement hydraulic motor, the motor must be sized, in terms of its displacement per revolution, for full break-out torque at the peak load position (as that term will be explained subsequently). At all loads less than the peak load, with motor flow being constant, excess power (fluid pressure) is dissipated within the control system. Thus, in order for the control system to achieve the full stroke of the flap within the specified time, the required size of the hydraulic motor results in the system operating at an excessive flow rate, during most of its operating cycle.
The requirement to size the motor to satisfy the peak load situation, while still achieving full stroke in the specified time, requires a hydraulic motor which is larger, more expensive, and heavier than is desirable. As will be understood by those skilled in any of the vehicle arts, excess size and weight of component s is always undesirable, but such is especially true in the case of aircraft.